In 1964, PWM was applied to AC speed control systems.
French scientists A. Schcnung and H. Stemmler were the first to propose applying pulse width modulation (PWM) technology from communication technology to AC speed control systems. Since then, research on PWM speed control technology has attracted considerable attention.
The world's first frequency converter was developed in 1967.
Vasa Control Systems GmbH of Finland, formerly known as STRONGB of Sweden, was founded in the 1960s. In 1967, it developed the world's first frequency converter and is known as the father of frequency converters, pioneering the world market for commercial frequency converters.
1968 Magnetic Field Orientation Control Theory
Dr. Haas, a German, first proposed the theory of magnetic field orientation control.
1971 Asynchronous Motor Rotor Field Oriented Vector Control Method
German scientist Berlaszczek proposed a rotor field-oriented vector control method for asynchronous motors, comparing it with that of DC and AC motors.
1995 DTC-controlled frequency converter
The first person in the world to propose DTC (Direct Controller) was German, and ABB produced the first DTC-controlled frequency converter in 1995.
1980s
Japanese scholars proposed a flux trajectory control method, making variable frequency and variable voltage technology (i.e., u/f control) the core of inverter technology. Researchers then continued to focus on further research into PWM technology, achieving the goal of voltage and frequency regulation.
General-purpose frequency converters began in 1992.
Siemens AG of Germany has successively developed the 6SE70 series of general-purpose frequency converters. Through the PE, VC, and SC boards, it can achieve frequency control, vector control, and servo control respectively, and also features torque control and trip-free performance. Its output static characteristics are significantly improved compared to ordinary U/f control general-purpose frequency converters. Its mechanical characteristics are stiffer than those of asynchronous motors powered by the mains frequency grid. This typical product belongs to the high-performance U/f control general-purpose frequency converter category. Based on this, a high-performance vector control general-purpose frequency converter has been developed and produced. This type of frequency converter has further improved dynamic performance.
In 1995, ABB first launched the direct torque control type general-purpose frequency converter.
It has now become a core technology for various series of general-purpose frequency converters. Its dynamic torque response has reached less than 2mm, and the static speed accuracy with a speed sensor is ±0.01%. Even without a speed sensor, a speed control accuracy of ±0.1% can be achieved. Other companies are also striving to achieve direct torque control.
Hitachi recently developed a dedicated integrated power module (ISPM) for general-purpose frequency inverters.
The rectifier circuit, inverter circuit, logic control, drive and protection circuits, and power supply circuit are all integrated into a single module. This significantly reduces the size of the general-purpose frequency converter and the number of leads. Advances in power electronic devices have greatly improved the performance of general-purpose frequency converters.
The Future of Frequency Converters
The main development focuses on further optimizing control technology, increasing capacity, reducing size, lowering costs, and reducing noise and electromagnetic pollution to the environment.
In areas where frequency converter development is still in its infancy
The control technology of frequency converters has evolved from U/f control to vector control and direct torque control, greatly improving the performance of AC speed control systems. However, some technologies still require in-depth research, such as the accurate estimation and observation of magnetic flux and the online identification of motor parameters.
Variable frequency technology has been around for decades, and the inverter system is relatively mature. However, how to break through the current state and open up further market opportunities is a question that every inverter manufacturer needs to consider in the future.
